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Portia
Portia is a small moon of Uranus. It is the only moon closer to Uranus then Puck with a diameter higher then 100 km. Known Characteristics Portia has a diameter of 135 km, orbits Uranus at 66000 km, has a rotation period of 0.513 Earth days and an estimated density of 1.3 kg/l. The orbit of Portia lies below Uranus's geosynchronous orbit. With other words, Portia orbits faster around Uranus then Uranus itself around its axis. Because of this, the orbit is slowly decaying, until Portia will break into a ring or will fall on Uranus. However, this process will take millions of years to happen. Portia is known to have a low albedo. This, combined with the low density, suggests that the moon is made of dirty water, water ice with many impurities, like carbon and organics (tholins). No spaceship imagined Portia close enough so that we can see details of its surface. We can only estimate some of the features that might exist. Portia orbits very close to one of Uranus's rings. It might be a shepherd moon, maintaining the ring in its place. This might suggest that Portia, like Saturn's ring moons, might be coated with soft material accreted from the ring. Also, the moon might be feeding the ring with debris ejected after meteorite impacts. Portia is a member of the Portia group, a group of moons sharing similar orbits. This might suggest that all moons were part of a larger body that crashed after a powerful impact. If this is true, the area around the moon should be filled with debris. However, like in case of the ring moons of Saturn, Daphnis and Pan, speed of particles around the moons is not high. Before Cassini arrived at Saturn, people believed that Saturn's rings are made of small asteroids that are continuously colliding. It was thought to be a very dangerous place. Today we know that the rings of Saturn are surprisingly calm. All their components rotate around the planet very slow with respect one to the other. We have reasons to believe this is also the case for Uranus. If particles in the ring are not moving fast, navigation is possible with a conventional ship. If Portia is a shepherd moon, then it exchanges matter with the ring. So, the materials on Portia's surface should have a similar composition with the materials in the ring. Colonization Portia is very close to Perdita, the moon which is the best destination for a space station in Uranus System. Flight routes between the two bodies don't imply too much Delta-v change. Portia is also close to the big moons of Uranus. However, the presence of a ring very close to Portia is a major challenge. Constant meteorite bombardment, even at low speeds, will affect any construction on Portia. The moon is too small to retain an atmosphere, so terraforming is out of question. The main constituents of Portia, water ice, tholins and carbon, are also found in large amounts on many other moons around Uranus. So, mining seems not feasible. Building a large industrial center on Portia is also not feasible, because of its closeness to the rings. It appears that the only possible revenue could come from tourism, just like in the cases of Saturn's ring moons Pan and Daphnis. Located close to the rings and offering an interesting view, Portia can become Uranus's number one touristic destination. Uranus is further away then Saturn and its rings are much smaller and darker then Saturn's. But even so, Portia can attract tourists as a cheaper destination. Category:Moons